Double-sided touch-sensitive panel with shield and drive combined layer

ABSTRACT

A multi-touch capacitive touch sensor panel can be created using a substrate with column and row traces formed on either side of the substrate. To shield the column (sense) traces from the effects of capacitive coupling from a modulated Vcom layer in an adjacent liquid crystal display (LCD) or any source of capacitive coupling, the row traces can be widened to shield the column traces, and the row traces can be placed closer to the LCD. In particular, the rows can be widened so that there is spacing of about 30 microns between adjacent row traces. In this manner, the row traces can serve the dual functions of driving the touch sensor panel, and also the function of shielding the more sensitive column (sense) traces from the effects of capacitive coupling.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 14/734,998, filed Jun. 9, 2015 (U.S. PatentApplication Publication No. 2015/0268772), which is a continuationapplication of U.S. patent application Ser. No. 14/340,262, filed Jul.24, 2014 (now U.S. Pat. No. 9,075,491, issued Jul. 7, 2015), which is acontinuation application of U.S. patent application Ser. No. 13/078,789,filed Apr. 1, 2011 (now U.S. Pat. No. 8,884,890, issued Nov. 11, 2014)which is a continuation of U.S. patent application Ser. No. 11/650,182,filed Jan. 3, 2007 (now U.S. Pat. No. 7,920,129, issued Apr. 5, 2011;re-examination Application No. 90/012,934, reexamination certificateissued Jul. 11, 2014) all of which are hereby incorporated by referencein their entirety for all purposes.

FIELD OF THE DISCLOSURE

This invention relates to touch sensor panels, and more particularly, tocapacitive multi-touch sensor panels having rows and columns formed oneither sides of the same substrate.

BACKGROUND OF THE DISCLOSURE

Many types of input devices are presently available for performingoperations in a computing system, such as buttons or keys, mice,trackballs, touch panels, joysticks, touch screens and the like. Touchscreens, in particular, are becoming increasingly popular because oftheir ease and versatility of operation as well as their decliningprice. Touch screens can include a touch panel, which can be a clearpanel with a touch-sensitive surface. The touch panel can be positionedin front of a display screen so that the touch-sensitive surface coversthe viewable area of the display screen. Touch screens can allow a userto make selections and move a cursor by simply touching the displayscreen via a finger or stylus. In general, the touch screen canrecognize the touch and position of the touch on the display screen, andthe computing system can interpret the touch and thereafter perform anaction based on the touch event.

Touch panels can include an array of touch sensors capable of detectingtouch events (the touching of fingers or other objects upon atouch-sensitive surface). Future panels may be able to detect multipletouches (the touching of fingers or other objects upon a touch-sensitivesurface at distinct locations at about the same time) and near touches(fingers or other objects within the near-field detection capabilitiesof their touch sensors), and identify and track their locations.Examples of multi-touch panels are described in Applicant's co-pendingU.S. application Ser. No. 10/842,862 entitled “Multipoint Touchscreen,”filed on May 6, 2004 and published as U.S. Published Application No.2006/0097991 on May 11, 2006, the contents of which are incorporated byreference herein.

Capacitive touch sensor panels can be formed from rows and columns oftraces on opposite sides of a dielectric. At the “intersections” of thetraces, where the traces pass above and below each other (but do notmake direct electrical contact with each other), the traces essentiallyform two electrodes. Conventional touch panels for use over displaydevices have typically utilized a top layer of glass upon whichtransparent column traces of indium tin oxide (ITO) or antimony tinoxide (ATO) have been etched, and a bottom layer of glass upon which rowtraces of ITO have been etched. However, the use of transparent tracesis not required if the conductors are thin enough (on the order of 30microns). In addition, if panel transparency is not required (e.g. thetouch panel is not being used over a display device), the conductors canbe made out of an opaque material such as copper. The top and bottomglass layers are separated by a clear polymer spacer that acts as adielectric between the row and column traces. The traces on both the topand bottom glass layers can have a spacing of about 5 mm.

To scan a sensor panel, a stimulus can be applied to one row with allother rows held at DC voltage levels. When a row is stimulated, amodulated output signal can be capacitively coupled onto the columns ofthe sensor panel. The columns can be connected to analog channels (alsoreferred to herein as event detection and demodulation circuits). Forevery row that is stimulated, each analog channel connected to a columngenerates an output value representative of an amount of change in themodulated output signal due to a touch or hover event occurring at thesensor located at the intersection of the stimulated row and theconnected column. After analog channel output values are obtained forevery column in the sensor panel, a new row is stimulated (with allother rows once again held at DC voltage levels), and additional analogchannel output values are obtained. When all rows have been stimulatedand analog channel output values have been obtained, the sensor panel issaid to have been “scanned,” and a complete “image” of touch or hovercan be obtained over the entire sensor panel. This image of touch orhover can include an analog channel output value for every pixel (rowand column) in the panel, each output value representative of the amountof touch or hover that was detected at that particular location.

Because the rows must be either stimulated with an AC signal or held ata DC voltage level, and because the columns must be connected to analogchannels so that modulated output signals can be detected, demodulatedand converted to output values, electrical connections must be formedwith the rows and columns on either side of the dielectric of the sensorpanel. Because the rows and columns are perpendicular to each other, themost straightforward way to connect to these rows and columns is to bonda flex circuit at one edge of the sensor panel (e.g. the shorter side ofa rectangular panel) to provide connections to the columns, and bondanother flex circuit on an adjacent edge of the sensor panel (e.g. thelonger side of a rectangular panel) to provide connections to the rows.However, because these flex circuit connections areas are not on thesame edge of the sensor panel and are not on directly opposing sides ofthe dielectric, the sensor panel must be made larger to accommodatethese two non-overlapping connection areas.

Furthermore, when a transparent capacitive touch sensor panel is bondedto a liquid crystal display (LCD), a modulated Vcom layer in the LCD cancouple onto the columns of the sensor panel, causing noise to appear onthe columns.

SUMMARY OF THE DISCLOSURE

A multi-touch sensor panel can be created using a substrate with columnand row traces formed on either side of the substrate using a novelfabrication process. Flex circuits can be used to connect the column androw traces on either side of the sensor panel to its associated sensorpanel circuitry. Traces made of copper or other highly conductive metalsrunning along the edge of the substrate can be used to bring the rowtraces to the same edge of the substrate as the column traces so thatthe flex circuits can be bonded to the same edge of the substrate ondirectly opposing sides of the substrate, minimizing the area needed forconnectivity and reducing the overall size of the sensor panel. A singleflex circuit can be fabricated to connect to the rows and columns ondirectly opposing sides at the same edge of the substrate. Furthermore,the row traces can be widened to shield the column traces from amodulated Vcom layer.

Column and row ITO traces can be formed on both sides of a DITOsubstrate using several fabrication methods. In one embodiment, asubstrate can be placed on the rollers of the fabrication machinery anda layer of ITO can be sputtered onto a first side of the DITO substrateand etched (e.g. using photolithography techniques) to form the columntraces. A protective coating of photoresist (e.g. two layers ofphotoresist) can then be applied over the column traces, and the DITOsubstrate can be flipped over so that the rollers make contact only withthe applied photoresist on the first side and not the formed columntraces. Another layer of ITO can then be sputtered onto the now-exposedback side of the DITO substrate and etched to form row traces 508.

If no metal traces are required, the photoresist on the first side canbe stripped off to complete the process. However, if metal traces arerequired at the edges to connect to the row traces and bring them to aparticular edge of the substrate, a protective coating of photoresist(e.g. two layers of photoresist) can be applied over the row traces,leaving the edges exposed. A metal layer can then be sputtered over thephotoresist and exposed edges, and the metal layer can then be etched toform metal traces at the edges. Finally, all remaining layers ofphotoresist can be stripped off.

Flex circuit portions on a single flex circuit can be formed forconnecting to the row and column traces, respectively, on either side ofa DITO substrate, and to a host processor. The flex circuit can alsoinclude a circuit area upon which a multi-touch subsystem, multi-touchpanel processor, high voltage driver and decoder circuitry, an EEPROMand some essential small components such as bypass capacitors can bemounted and connected to save space.

The rows of the DITO substrate can also be widened for shieldingpurposes and for providing a uniform appearance according to embodimentsof this invention. To prevent the capacitive coupling of a modulatedVcom layer onto the columns of the substrate, the rows may be widened.The number of rows does not change, but they can be much wider, leavingonly about 30 microns of space between them. Because these wider rowsare not isolated but are instead either held at a DC voltage orstimulated with a stimulation voltage, these wider rows act as a shield,preventing a modulated Vcom layer from capacitively coupling onto thecolumns. In addition, because of the narrow spacing between them, thewide rows provide a uniform appearance. Thus, shielding, modulation anda uniform appearance can be obtained from a single layer of ITO.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary computing system operable with acapacitive multi-touch sensor panel according to one embodiment of thisinvention.

FIG. 2a illustrates an exemplary capacitive multi-touch panel accordingto one embodiment of this invention.

FIG. 2b is a side view of exemplary pixel in a steady-state (no-touch)condition according to one embodiment of this invention.

FIG. 2c is a side view of exemplary pixel in a dynamic (touch) conditionaccording to one embodiment of this invention.

FIG. 3 is an exploded perspective view of an exemplary capacitive touchsensor panel formed from a top layer of glass upon which transparentcolumn traces of ITO have been etched, and a bottom layer of glass uponwhich row traces of ITO have been etched.

FIG. 4 illustrates an exemplary capacitive touch sensor panel fabricatedusing a double-sided ITO (DITO) substrate having column and row ITOtraces formed on either side of the substrate, and bonded between acover and an LCD using transparent adhesive according to one embodimentof this invention.

FIG. 5 is an exploded perspective view of an exemplary DITO substrate(with its thickness greatly exaggerated for purposes of illustrationonly) with columns and rows formed on either side according to oneembodiment of this invention.

FIG. 6 illustrates an exemplary flex circuit according to one embodimentof this invention, including flex circuit portions for connecting to therow and column traces, respectively, on either side of a DITO substrate,and a flex circuit portion for connecting to a host processor.

FIG. 7 is an exploded perspective view of an exemplary DITO substrate(with its thickness greatly exaggerated for purposes of illustrationonly) with columns and rows formed on either side, and small isolatedsquares between the columns and rows to provide a uniform appearance.

FIG. 8 illustrates a stackup of an exemplary double-sided touch panelalong with a cover and liquid crystal display (LCD) according to oneembodiment of this invention.

FIG. 9 is a perspective view of an exemplary DITO substrate (with itsthickness greatly exaggerated for purposes of illustration only)illustrating the widening of rows for shielding purposes and forproviding a uniform appearance according to one embodiment of thisinvention.

FIG. 10a illustrates an exemplary mobile telephone that can include thecapacitive touch sensor panel and a flex circuit capable of connectingto both sides of the substrate according to one embodiment of thisinvention.

FIG. 10b illustrates an exemplary digital audio player that can includethe capacitive touch sensor panel and a flex circuit capable ofconnecting to both sides of the substrate according to one embodiment ofthis invention.

DETAILED DESCRIPTION

In the following description of preferred embodiments, reference is madeto the accompanying drawings which form a part hereof, and in which itis shown by way of illustration specific embodiments in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the preferred embodiments of the presentinvention.

Multi-touch sensor panels and their associated sensor panel circuitrymay be able to detect multiple touches (touch events or contact points)that occur at about the same time, and identify and track theirlocations. FIG. 1 illustrates exemplary computing system 100 operablewith capacitive multi-touch sensor panel 124 according to embodiments ofthis invention. Multi-touch sensor panel 124 can be created using asubstrate with column and row traces formed on either side of thesubstrate using a novel fabrication process. Flex circuits can be usedto connect the column and row traces on either side of the sensor panelto its associated sensor panel circuitry. Traces made of copper or otherhighly conductive metals running along the edge of the substrate can beused to bring the row traces to the same edge of the substrate as thecolumn traces so that the flex circuits can be bonded to the same edgeof the substrate on directly opposing sides of the substrate, minimizingthe area needed for connectivity and reducing the overall size of thesensor panel. A single flex circuit can be fabricated to connect to therows and columns on directly opposing sides at the same edge of thesubstrate. Furthermore, the row traces can be widened to shield thecolumn traces from a modulated Vcom layer.

Computing system 100 can include one or more panel processors 102 andperipherals 104, and panel subsystem 106. The one or more processors 102can include, for example, an ARM968 processors or other processors withsimilar functionality and capabilities. However, in other embodiments,the panel processor functionality can be implemented instead bydedicated logic such as a state machine. Peripherals 104 can include,but are not limited to, random access memory (RAM) or other types ofmemory or storage, watchdog timers and the like.

Panel subsystem 106 can include, but is not limited to, one or moreanalog channels 108, channel scan logic 110 and driver logic 114.Channel scan logic 110 can access RAM 112, autonomously read data fromthe analog channels and provide control for the analog channels. Thiscontrol can include multiplexing columns of multi-touch panel 124 toanalog channels 108. In addition, channel scan logic 110 can control thedriver logic and stimulation signals being selectively applied to rowsof multi-touch panel 124. In some embodiments, panel subsystem 106,panel processor 102 and peripherals 104 can be integrated into a singleapplication specific integrated circuit (ASIC).

Driver logic 114 can provide multiple panel subsystem outputs 116 andcan present a proprietary interface that drives high voltage driver,which is comprised of decoder 120 and subsequent level shifter anddriver stage 118, although level-shifting functions could be performedbefore decoder functions. Level shifter and driver 118 can provide levelshifting from a low voltage level (e.g. CMOS levels) to a higher voltagelevel, providing a better signal-to-noise (S/N) ratio for noisereduction purposes. Decoder 120 can decode the drive interface signalsto one out of N outputs, whereas N is the maximum number of rows in thepanel. Decoder 120 can be used to reduce the number of drive linesneeded between the high voltage driver and panel 124. Each panel rowinput 122 can drive one or more rows in panel 124. In some embodiments,driver 118 and decoder 120 can be integrated into a single ASIC.However, in other embodiments driver 118 and decoder 120 can beintegrated into driver logic 114, and in still other embodiments driver118 and decoder 120 can be eliminated entirely.

Computing system 100 can also include host processor 128 for receivingoutputs from panel processor 102 and performing actions based on theoutputs that can include, but are not limited to, moving an object suchas a cursor or pointer, scrolling or panning, adjusting controlsettings, opening a file or document, viewing a menu, making aselection, executing instructions, operating a peripheral deviceconnected to the host device, answering a telephone call, placing atelephone call, terminating a telephone call, changing the volume oraudio settings, storing information related to telephone communicationssuch as addresses, frequently dialed numbers, received calls, missedcalls, logging onto a computer or a computer network, permittingauthorized individuals access to restricted areas of the computer orcomputer network, loading a user profile associated with a user'spreferred arrangement of the computer desktop, permitting access to webcontent, launching a particular program, encrypting or decoding amessage, and/or the like. Host processor 128 can also perform additionalfunctions that may not be related to panel processing, and can becoupled to program storage 132 and display device 130 such as a liquidcrystal display (LCD) for providing a UI to a user of the device.

As mentioned above, multi-touch panel 124 can in some embodimentsinclude a capacitive sensing medium having a plurality of row traces ordriving lines and a plurality of column traces or sensing lines(although other sensing media may also be used) separated by adielectric. In some embodiments, the dielectric material can betransparent, such as glass, or can be formed from other materials suchas Mylar. The row and column traces can be formed from a transparentconductive medium such as ITO or ATO, although other transparent ornon-transparent materials such as copper can also be used. In someembodiments, the row and column traces can be perpendicular to eachother, although in other embodiments other non-orthogonal andnon-Cartesian orientations are possible. For example, in a polarcoordinate system, the sensing lines can be concentric circles and thedriving lines can be radially extending lines (or vice versa). It shouldbe understood, therefore, that the terms “row” and “column,” “firstdimension” and “second dimension,” or “first axis” and “second axis” asmay be used herein are intended to encompass not only orthogonal grids,but the intersecting traces of other geometric configurations havingfirst and second dimensions (e.g. the concentric and radial lines of apolar-coordinate arrangement).

At the “intersections” of the traces, where the traces pass above andbelow each other (but do not make direct electrical contact with eachother), the traces essentially form two electrodes (although more thantwo traces could intersect as well). Each intersection of row and columntraces can represent a capacitive sensing node and can be viewed aspicture element (pixel) 126, which can be particularly useful whenmulti-touch panel 124 is viewed as capturing an “image” of touch. (Inother words, after multi-touch subsystem 106 has determined whether atouch event has been detected at each touch sensor in the multi-touchpanel, the pattern of touch sensors in the multi-touch panel at which atouch event occurred can be viewed as an “image” of touch (e.g. apattern of fingers touching the panel).) The capacitance between row andcolumn electrodes appears as a stray capacitance on all columns when thegiven row is held at DC and as a mutual capacitance Csig when the givenrow is stimulated with an AC signal. The presence of a finger or otherobject near or on the multi-touch panel can be detected by measuringchanges to Csig. The columns of multi-touch panel 124 can drive one ormore analog channels 108 (also referred to herein as event detection anddemodulation circuits) in multi-touch subsystem 106. In someembodiments, each column is coupled to one dedicated analog channel 108.However, in other embodiments, the columns may be couplable via ananalog switch to a fewer number of analog channels 108.

FIG. 2a illustrates exemplary capacitive multi-touch panel 200. FIG. 2aindicates the presence of a stray capacitance Cstray at each pixel 202located at the intersection of a row 204 and a column 206 trace(although Cstray for only one column is illustrated in FIG. 2 forpurposes of simplifying the figure). Note that although FIG. 2aillustrates rows 204 and columns 206 as being substantiallyperpendicular, they need not be so aligned, as described above. In theexample of FIG. 2a , AC stimulus Vstim 214 is being applied to one row,with all other rows connected to DC. The stimulus causes a charge to beinjected into the column electrodes through mutual capacitance at theintersecting points. This charge is Qsig=Csig×Vstm. Each of columns 206may be selectively connectable to one or more analog channels (seeanalog channels 108 in FIG. 1).

FIG. 2b is a side view of exemplary pixel 202 in a steady-state(no-touch) condition. In FIG. 2b , an electric field of electric fieldlines 208 of the mutual capacitance between column 206 and row 204traces or electrodes separated by dielectric 210 is shown.

FIG. 2c is a side view of exemplary pixel 202 in a dynamic (touch)condition. In FIG. 2c , finger 212 has been placed near pixel 202.Finger 212 is a low-impedance object at signal frequencies, and has anAC capacitance Cfinger from the column trace 206 to the body. The bodyhas a self-capacitance to ground Cbody of about 200 pF, where Cbody ismuch larger than Cfinger. If finger 212 blocks some electric field lines208 between the row and column electrodes (those fringing fields thatexit the dielectric and pass through the air above the row electrode),those electric field lines are shunted to ground through the capacitancepath inherent in the finger and the body, and as a result, the steadystate signal capacitance Csig is reduced by ΔCsig. In other words, thecombined body and finger capacitance act to reduce Csig by an amountΔCsig (which can also be referred to herein as Csig_sense), and can actas a shunt or dynamic return path to ground, blocking some of theelectric fields as resulting in a reduced net signal capacitance. Thesignal capacitance at the pixel becomes Csig-ΔCsig, where Csigrepresents the static (no touch) component and ΔCsig represents thedynamic (touch) component. Note that Csig-ΔCsig may always be nonzerodue to the inability of a finger, palm or other object to block allelectric fields, especially those electric fields that remain entirelywithin the dielectric material. In addition, it should be understoodthat as a finger is pushed harder or more completely onto themulti-touch panel, the finger can tend to flatten, blocking more andmore of the electric fields, and thus ΔCsig can be variable andrepresentative of how completely the finger is pushing down on the panel(i.e. a range from “no-touch” to “full-touch”).

Referring again to FIG. 2a , as mentioned above, Vstim signal 214 can beapplied to a row in multi-touch panel 200 so that a change in signalcapacitance can be detected when a finger, palm or other object ispresent. Vstim signal 214 can be generated as one or more pulse trains216 at a particular frequency, with each pulse train including a numberof pulses. Although pulse trains 216 are shown as square waves, otherwaveshapes such as sine waves can also be employed. A plurality of pulsetrains 216 at different frequencies can be transmitted for noisereduction purposes to detect and avoid noisy frequencies. Vstim signal214 essentially injects a charge into the row, and can be applied to onerow of multi-touch panel 200 at a time while all other rows are held ata DC level. However, in other embodiments, the multi-touch panel can bedivided into two or more sections, with Vstim signal 214 beingsimultaneously applied to one row in each section and all other rows inthat region section held at a DC voltage.

Each analog channel coupled to a column measures the mutual capacitanceformed between that column and the row. This mutual capacitance iscomprised of the signal capacitance Csig and any change Csig_sense inthat signal capacitance due to the presence of a finger, palm or otherbody part or object. These column values provided by the analog channelsmay be provided in parallel while a single row is being stimulated, ormay be provided in series. If all of the values representing the signalcapacitances for the columns have been obtained, another row inmulti-touch panel 200 can be stimulated with all others held at a DCvoltage, and the column signal capacitance measurements can be repeated.Eventually, if Vstim has been applied to all rows, and the signalcapacitance values for all columns in all rows have been captured (i.e.the entire multi-touch panel 200 has been “scanned”), a “snapshot” ofall pixel values can be obtained for the entire multi-touch panel 200.This snapshot data can be initially saved in the multi-touch subsystem,and later transferred out for interpretation by other devices in thecomputing system such as the host processor. As multiple snapshots areobtained, saved and interpreted by the computing system, it is possiblefor multiple touches to be detected, tracked, and used to perform otherfunctions.

As described above, because the rows may be either stimulated with an ACsignal or held at a DC voltage level, and because the columns need to beconnected to analog channels so that modulated output signals can bedetected, demodulated and converted to output values, electricalconnections must be formed with the rows and columns on either side ofthe dielectric of the sensor panel.

FIG. 3 is an exploded perspective view of an exemplary capacitive touchsensor panel 300 formed from a top layer of glass 302 upon whichtransparent column traces of ITO 304 have been etched, and a bottomlayer of glass 306 upon which row traces of ITO 308 have been etched.The top and bottom glass layers 302 and 306 are separated by a clearpolymer spacer 310 that acts as a dielectric between the row and columntraces. Because the rows and columns are perpendicular to each other,the most straightforward way to connect to these rows and columns is tobond flex circuit 312 at one edge of the sensor panel, and bond anotherflex circuit 314 on an adjacent edge of the sensor panel. However,because the connection areas for these flex circuits 312 and 314 are noton the same edge of sensor panel 300 and are not on directly opposingsides of dielectric 310, the sensor panel must be made larger toaccommodate these two non-overlapping connection areas.

Capacitive touch sensor panels typically form the row and column traceson two pieces of glass as shown in FIG. 3 because it has not beenpractical to form column and row traces on either side of a singlesubstrate. Conventional methods for forming ITO traces on one side of asubstrate require that the substrate be placed on rollers during thefabrication process. However, if the substrate is then flipped over toform ITO traces on the second side, the rollers will damage any tracespreviously formed on the first side of the substrate. Furthermore, whenetching is used to etch away part of the ITO to form traces on one sideof the substrate, the entire substrate is conventionally placed in anetching bath, which will etch away any traces previously formed on theother side of the substrate.

FIG. 4 illustrates an exemplary capacitive touch sensor panel 400fabricated using a double-sided ITO (DITO) substrate 402 having columnand row ITO traces 404 and 406, respectively, formed on either side ofthe substrate, and bonded between cover 408 and LCD 410 usingtransparent adhesive 412 according to embodiments of this invention.Substrate 402 can be formed from glass, plastic, hybrid glass/plasticmaterials, and the like. Cover 408 can be formed from glass, acrylic,sapphire, and the like. To connect to column and row traces 404 and 406,respectively, two flex circuit portions 414 can be bonded to directlyopposing sides at the same edge of DITO 402, although other bondinglocations may also be employed.

FIG. 5 is an exploded perspective view of an exemplary DITO substrate500 (with its thickness greatly exaggerated for purposes of illustrationonly) with columns 502 and rows 508 formed on either side according toembodiments of this invention. Some of column ITO traces 502 on the topside are routed to a necked-down connector area 504, where they arebrought off the panel by a flex circuit portion 506 that can beconductively bonded to the top of DITO substrate 500. In someembodiments, row ITO traces 508 on the bottom side can be connected tothin metal traces 510 that run alongside the edges of the bottom side.Metal traces 510 can be routed to connector area 512, which can bedirectly opposing connector area 504, or at least on the same edge ofDITO substrate 500 as connector area 504. Providing connector areas 504and 512 at the same edge of DITO substrate 500 can allow the substrateand therefore the product to be smaller. Another flex circuit portion514 can be used to bring row ITO traces 508 off the panel.

Column and row ITO traces 502 and 508 can be formed on both sides ofDITO substrate 500 using several fabrication methods. In one embodiment,a substrate can be placed on the rollers of the fabrication machineryand a layer of ITO can be sputtered onto a first side of DITO substrate500 and etched (e.g. using photolithography techniques) to form columntraces 502. A protective coating of photoresist (e.g. two layers ofphotoresist) can then be applied over the column traces 502, and DITOsubstrate 500 can be flipped over so that the rollers make contact onlywith the applied photoresist on the first side and not the formed columntraces. Another layer of ITO can then be sputtered onto the now-exposedback side of DITO substrate 500 and etched to form row traces 508.

If no metal traces 510 are required, the photoresist on the first sidecan be stripped off to complete the process. However, if metal traces510 are required at the edges to connect to row traces 508 and bringthem to a particular edge of the substrate, a protective coating ofphotoresist (e.g. two layers of photoresist) can be applied over rowtraces 508, leaving the edges exposed. A metal layer can then besputtered over the photoresist and exposed edges, and the metal layercan then be etched to form metal traces 510 at the edges. Finally, allremaining layers of photoresist can be stripped off.

Minor variations to the process described above can also be made. Forexample, the second side of the DITO substrate patterning may be formedby first patterning a photoresist using very simple geometry to coveronly the interior region of the second side of the DITO substrate whileleaving the edge regions exposed. For this variation, metal is sputteredfirst and then the photoresist with simple geometry is then stripped offto leave metal in the edge regions only. Then the ITO is sputtered overthe entire second side of the DITO substrate. A second photoresist isapplied and patterned to form the mask for the electrode patterns. Aseries of etching steps is then used to form the electrode pattern inthe topmost ITO layer and metal layer underneath. The first etchingsteps etches the ITO only, and the second etch steps etches the metallayer only which produces the desired electrode geometry.

FIG. 6 illustrates an exemplary flex circuit 600 according toembodiments of this invention, including flex circuit portions 606 and614 for connecting to the row and column traces, respectively, on eitherside of a DITO substrate, and flex circuit portion 608 for connecting toa host processor. Flex circuit 600 includes a circuit area 602 uponwhich the multi-touch subsystem, multi-touch panel processor, the highvoltage driver and decoder circuitry (see FIG. 1), an EEPROM and someessential small components such as bypass capacitors can be mounted andconnected to save space. Circuit area 602 may be shielded by an EMI can(not shown) which encloses circuit area 602 using top and bottom shieldportions. The bottom can may be adhered to a structure of the device tosecure the circuit area. From this circuit area 602, flex circuit 600may connect to the top of the DITO substrate via flex circuit portion606, to the bottom of the DITO substrate via flex circuit portion 614,and to a host processor via flex circuit portion 608.

FIG. 7 is an exploded perspective view of an exemplary DITO substrate700 (with its thickness greatly exaggerated for purposes of illustrationonly) with columns 702 and rows 708 formed on either side. As shown inFIG. 7, column traces 702 can be about 1 mm wide, with a spacing ofabout 4 mm between the traces, and row traces 708 can be about 2 mmwide, with a spacing of about 3 mm between the rows. To create a moreuniform appearance, small isolated squares of ITO 704 can be formedbetween the column and row traces 702 and 708 on either side of DITOsubstrate 700, with narrow spacing (e.g. about 30 microns) between theisolated squares of ITO, so that either side of the DITO substrateprovides a uniform appearance similar to a solid sheet of ITO.

FIG. 8 illustrates a stackup of an exemplary double-sided touch panel800 along with cover 802 and liquid crystal display (LCD) 804 accordingto embodiments of this invention. From top to bottom, LCD 804 caninclude polarizer 806, top glass layer 808, liquid crystal layer 810,bottom glass layer 812, polarizer 814, and backlight 816.

From top to bottom, liquid crystal layer 810 can include RGB colorfilter layer 818, planarization layer 820, a conductive unpatternedlayer of ITO referred to as Vcom layer 822, polyamide layer 824, liquidcrystal layer 826, and polyamide layer 828. Beneath polyamide layer 828is a layer of ITO rectangles and TFTs (collectively referred to hereinas TFT layer 830), with one ITO rectangle and TFT for each sub-pixel(where three sub-pixels comprise a pixel).

Color filter layer 818 provides the three RGB colors that make up eachpixel when illuminated by light, wherein the ratio of colors determinesthe color of that pixel. Planarization layer 820 can be formed fromclear plastic to smooth out the surface of color filter layer 818. Vcomstands for “Voltage common” because Vcom layer 822 provides a commonvoltage for the ITO subpixels of TFT layer 830. Vcom layer 822 may bemaintained at a constant voltage (LCDs using a constant Vcom voltage maybe referred to as DC or constant Vcom LCDs) or modulated with an ACsignal. Polyamide layers 824 and 828 serve to pre-align the orientationof liquid crystals in liquid crystal layer 826. To create the color forone pixel, the ITO squares for each subpixel in TFT layer 830 can havevoltages applied to them with respect to Vcom layer 822, which causesthe liquid crystals to align and allow light from backlight 816 to passthrough liquid crystal layer 826 and through the RGB color filters incolor filter layer 818.

As mentioned above, although Vcom layer 822 can be held constant, insome embodiments the Vcom layer can be driven by a modulated signal(e.g. a squareware from about 1 to 4 volts). However, when Vcom layer822 is driven by a modulated signal, the modulated signal may becapacitively coupled (see reference character 834) through the sparseconductors of rows 836 on the bottom of double-sided touch panel 800 andonto columns 838, causing noise on the columns. Note that rows 836 arereferred to as “sparse,” even though it includes many closely spaced ITOsquares, because the squares are isolated and therefore of negligibleeffect from a shielding standpoint. Note also that although modulatedVcom layer 822 is also capacitively coupled onto rows 836, because therows are being driven by driver circuitry with low impedance outputs,any capacitive coupling is shunted to the driver outputs, and hasnegligible effect. However, columns 838 are designed to sense smallchanges in the AC capacitance of the touch panel, so the capacitivecoupling from modulated Vcom layer 822 can easily be seen as noise atthe analog channels receiving the columns.

FIG. 9 is a perspective view of an exemplary DITO substrate 900 (withits thickness greatly exaggerated for purposes of illustration only)illustrating the widening of rows 936 for shielding purposes and forproviding a uniform appearance according to embodiments of thisinvention. To prevent the capacitive coupling of a modulated Vcom layeronto columns 938, rows 936 may be widened as shown in FIG. 9. The numberof rows 936 does not change, but they are now much wider (e.g. about4.97 mm), leaving only about 30 microns of space between them. Becausethese wider rows 936 are not isolated but are instead either held at aDC voltage or stimulated with a stimulation voltage, these wider rows936 act as a shield, preventing a modulated Vcom layer from capacitivelycoupling onto columns 938. In addition, because of the narrow spacingbetween them, rows 936 provide a uniform appearance. Thus, shielding,modulation and a uniform appearance can be obtained from a single layerof ITO. Note that although FIG. 9 illustrates rows and columns formed onopposite sides of a single substrate, wide rows can also be employed onthe otherwise conventional touch sensor panel shown in FIG. 3. Analternative to these wide rows is to add another layer of ITO as ashield between the LCD and DITO, but this would represent extra cost,extra thickness, light loss, and unwanted color shift.

As mentioned above, top side of an exemplary DITO substrate according toembodiments of the invention may include isolated ITO squares betweenrows, and a bottom side may include wide rows. Outer row traces can berouted to a first flex connector area on the top side via traces. Rowson the bottom side can be routed to second flex connector areas viametal traces running along the long edges of the bottom side. Note thatthe second flex connector areas can be located on the same edge of theDITO substrate as the first flex connector, but the conductorsthemselves are located in non-overlapping areas to make bonding of flexcircuits easier.

FIG. 10a illustrates an exemplary mobile telephone 1136 that can includecapacitive touch sensor panel 1124 and flex circuit 1134 capable ofconnecting to both sides of the substrate according to embodiments ofthis invention. Sensor panel 1124 can be fabricated using a substratehaving column and row ITO traces formed on either side of the substrate,and metal traces form along the edges of one side of the substrate toallow flex circuit connection areas to be located on opposing sides ofthe same edge of the substrate. Furthermore, sensor panel 1124 can befabricated with wide rows to provide modulated Vcom layer shielding aswell as a uniform appearance. FIG. 10b illustrates an exemplary digitalaudio/video player 1138 that can include capacitive touch sensor panel1124 and flex circuit 1134 capable of connecting to both sides of thesubstrate according to embodiments of this invention. Sensor panel 1124can be fabricated using a substrate having column and row ITO tracesformed on either side of the substrate, and metal traces form along theedges of one side of the substrate to allow flex circuit connectionareas to be located on opposing sides of the same edge of the substrate.Furthermore, sensor panel 1124 can be fabricated with wide rows toprovide modulated Vcom layer shielding as well as a uniform appearance.The mobile telephone and digital audio/video player of FIGS. 10a and 10bcan advantageously benefit from sensor panel 1124 because a single,thinner, smaller-sized sensor panel can be used, and only a single layerof ITO is needed to provide shielding and a uniform appearance. Theoverall effect is reduced product size and manufacturing costs.

Although the present invention has been fully described in connectionwith embodiments thereof with reference to the accompanying drawings, itis to be noted that various changes and modifications will becomeapparent to those skilled in the art. Such changes and modifications areto be understood as being included within the scope of the presentinvention as defined by the appended claims.

What is claimed is:
 1. A touch sensor panel, comprising: a first set ofco-planar traces of conductive material, a total surface area of thefirst set of co-planar traces defining a first surface area; and asecond set of co-planar traces of the conductive material formed on adifferent plane from the first set of co-planar traces, the totalsurface area of the second set of co-planar traces defining a secondsurface area; wherein the second set of co-planar traces are configuredfor being held at a DC voltage or stimulated with a stimulation voltageto provide shielding from electrical interference for the first set ofco-planar traces.
 2. The touch sensor panel of claim 1, wherein thesecond set of co-planar traces are switchably couplable for receivingthe DC voltage or the stimulation voltage.
 3. The touch sensor panel ofclaim 1, wherein sensors are formed at locations at which the first setof co-planar traces cross over the second set of co-planar traceswithout making direct electrical contact.
 4. The touch sensor panel ofclaim 1, wherein the second surface area is greater than the firstsurface area.
 5. The touch sensor panel of claim 1, wherein the secondset of co-planar traces are configured to provide an average spacingbetween individual traces of the second set of co-planar traces of lessthan a predetermined amount to provide optical uniformity.
 6. The touchsensor panel of claim 1, the touch sensor panel supported on a liquidcrystal display (LCD) capable of emitting a modulated signal, whereinthe second set of co-planar traces is configured for shielding the firstset of co-planar traces from the modulated signal.
 7. The touch sensorpanel of claim 1, wherein the second set of co-planar traces areconfigured to provide shielding from capacitive coupling.
 8. The touchsensor panel of claim 1, the touch sensor panel coupled to a panelsubsystem controller configured for sending the DC voltage or thestimulation voltage to the second set of co-planar traces and receivingsense signals from the first set of co-planar traces.
 9. The touchsensor panel of claim 1, the touch sensor panel incorporated into atouch-sensitive computing system.
 10. A touch sensor panel, comprising:a plurality of sense traces of conductive material having a totalsurface area defining a first surface area; and a plurality of drivetraces of the conductive material spatially separated from the pluralityof sense traces, the plurality of drive traces having a total surfacearea defining a second surface area; wherein the plurality of drivetraces are configured for being held at a DC voltage or stimulated witha stimulation voltage to provide shielding from electrical interferencefor the plurality of sense traces.
 11. The touch sensor panel of claim10, wherein the plurality of drive traces are switchably couplable forreceiving the DC voltage or the stimulation voltage.
 12. The touchsensor panel of claim 10, wherein sensors are formed at locations atwhich the plurality of sense traces cross over the plurality of drivetraces pass without making direct electrical contact.
 13. The touchsensor panel of claim 10, wherein the second surface area is greaterthan the first surface area.
 14. The touch sensor panel of claim 10,wherein the plurality of drive traces are configured to provide anaverage spacing between individual traces of the plurality of drivetraces of less than a predetermined amount to provide opticaluniformity.
 15. The touch sensor panel of claim 10, the touch sensorpanel supported on a liquid crystal display (LCD) capable of emitting amodulated signal, wherein the plurality of drive traces are configuredfor shielding the plurality of sense traces from the modulated signal.16. The touch sensor panel of claim 10, wherein the plurality of drivetraces are configured to provide shielding from capacitive coupling. 17.The touch sensor panel of claim 10, the touch sensor panel coupled to apanel subsystem controller configured for sending the DC voltage or thestimulation voltage to the plurality of drive traces and receiving sensesignals from the plurality of sense traces.
 18. The touch sensor panelof claim 10, the touch sensor panel incorporated into a touch-sensitivecomputing system.
 19. A method for shielding a touch sensor panel,comprising: interposing a second layer of conductive material includinga plurality of second traces between a first layer of the conductivematerial including a plurality of first traces and a noise source, theplurality of second traces having a total surface area defining a secondsurface area and the plurality of first traces having a total surfacearea defining a first surface area; and biasing the plurality of secondtraces with a DC voltage or a stimulation voltage to provide shieldingfrom electrical interference for the plurality of first traces.
 20. Themethod of claim 19, further comprising switchably coupling the pluralityof second traces to receive either the DC voltage or the stimulationvoltage.
 21. The method of claim 19, further comprising arranging theplurality of second traces and the plurality of first traces to formsensors at locations at which the plurality of second traces cross underthe plurality of first traces without making direct electrical contact.22. The method of claim 19, wherein the second surface area is greaterthan the first surface area.
 23. The method of claim 19, furthercomprising configuring the plurality of second traces to provide anaverage spacing between individual traces of the plurality of secondtraces of less than a predetermined amount to provide opticaluniformity.
 24. The method of claim 19, further comprising: supportingthe touch sensor panel on a liquid crystal display (LCD) capable ofemitting a modulated signal; and shielding the plurality of first tracesfrom the modulated signal using the plurality of second traces.
 25. Themethod of claim 19, further comprising biasing the plurality of secondtraces to provide shielding from capacitive coupling for the pluralityof first traces.